Contemporary sheet substrate media edge sensors include a light emitter as well as a receiver for detecting the emitted light. As shown in FIG. 7, a sensor 120 is disposed along the sheet travel path P and disposed to radiate light across two baffles 110, 112 for guiding sheet movement there between. The shortest distance from the lower baffle 112 to sheet is referred to as the “fly height” of the sheet. The sensor 120 includes a light emitter 122 that transmits a cone-shaped beam of light 123 which is radiated expanding outwardly in a cone-shape toward a reflector 114 that also generates a cone-shaped reflection beam 124 heading back towards the sensor's detector 128. The sensor 120 detects the presence of a sheet when light no longer reaches the detector 128, generally because the sheet has blocked the light 124. The first instance that the detector 128 stops receiving a signal is generally associated with the arrival of the leading edge of a sheet. It should also be understood that the inverse would be true for timing the trailing edge of a sheet passing a particular point in the system. The angled outer edges of at least the reflected light cause the receiver to detect the presence of a sheet at different times depending on how high the sheet is traveling along the media path (fly height). Thus, a sheet with a higher fly height 15 will start blocking the light 124 earlier along the sheet path P than a sheet with a lower fly height 16. In this way, any deviation from a sheet traveling at a fly height that is equidistant from both the upper and lower baffles 110, 112, will yield an error in detecting the position of a sheet at the point of arrival (when it is first detected by the sensor). This error is referred to herein as fly height error. This effect causes any trailing edge measurements to also have errors due to fly height. Measurements of a typical sensor 120 will have as much as 0.2 mm of error, based on a 3 mm variation in sheet fly height.
One contemporary solution to such leading edge fly height errors is to angle the sensor such that the outer conical edge of the receiving beam has a more vertical configuration, thus minimizing the fly height error. However, such a configuration while reducing leading edge fly height errors, makes errors relating to trailing edge detection even worse. Accordingly, the angled sensor configuration is typically not used for trailing edge sensing.
Accordingly, it would be desirable to provide a system and/or method which can have precise sheet edge sensing and thus overcomes the shortcoming of the prior art. In particular, a system and/or method in accordance with aspects of the disclosed technologies preferably reduces fly height error and enables accurate leading and trailing edge detection, sheet registration, sheet size detection and other sheet handling functions.